ACTIVITY AND ELECTROPHORETIC CHARACTERIZATION OF ESTERASES IN INSECTICIDE-RESISTANT AND SUSCEPTIBLE STRAINS OF GERMAN-COCKROACH (DICTYOPTERA, BLATTELLIDAE)

Strains of German cockroach, Blattella germanica (L.), were tested for resistance to three insecticides using the time-mortality response te chnique in comparison with known susceptible strains. Dursban-R and Ma cy strains indicated high levels of resistance to chlorpyrifos and mod erate resistance to propoxur and cypermethrin. The hydrolytic activity of esterase enzymes was determined with a model substrate, p-nitrophe nyl acetate. The specific activity of the enzymes increased with a cor responding increase in substrate concentration. Maximum activity was o bserved an 80 muM. The resistant strains had significantly higher acti vity than the susceptible strains. The enzyme activity also increased with an increase in pH. Highest esterase activity was observed at pH 8 .0 for all the strains. The calculated Michaelis Menten constant (K(m) ) values for the resistant strains were nearly two-fold higher than fo r the susceptible strains. Nondenaturing gel electrophoresis revealed differences in isozyme composition. In total, 10 esterase bands were d etected, and these bands were characterized using different inhibitors and substrates.